The present invention relates to a system and method for cooling an engine, and more particularly, to a system and method for cooling an engine by separately cooling an engine""s cylinder block and cylinder head.
An internal combustion engine produces power by burning fuel in air. Accordingly, such engines are typically provided with cooling systems to radiate heat produced during the combustion away from the engine. Two types of cooling systems are widely used, namely, water-cooled systems and an air-cooled systems. Air-cooled systems cool the engine by flow of air, while water-cooled systems cool the engine by forcing coolant through the engine.
FIG. 1 shows a typical construction of a water-cooled system.
An engine 100 includes a cylinder head 110 and a cylinder block 120, where the cylinder head 110 and the cylinder block 120 respectively have first and second water-jackets 115 and 125. The first and second water-jackets 115 and 125 are connected and open to each other such that cylinders (not shown) and combustion chambers (not shown) are enclosed by the first and second water jackets 115 and 125. The first and second water-jackets 115 and 125 are usually collectively called the water-jacket.
A water-cooled cooling system includes a radiator 150 for cooling the coolant. Hot coolant is supplied from the water-jackets 115 and 125 to the radiator 150 through a high-temperature coolant line 130. The coolant, once cooled at the radiator 150, returns to the engine 100 through a low-temperature coolant line 140. A hydraulic pump 160 for generating such coolant flow is provided at a portion of the engine 100.
When the engine 100 is initially started, the coolant does not have to be cooled because its temperature is low. In fact, the coolant flow is generally blocked to quickly increase the coolant temperature. For this reason, a thermostat 170 is provided at a predetermined position in one of the high-temperature coolant line 130 and the low-temperature coolant line 140. The thermostat 170 opens the coolant line when the coolant temperature is above a predetermined temperature, and closes the coolant line when the coolant temperature is below the predetermined temperature. As shown in FIG. 1, the thermostat 170 can be disposed along either the high-temperature coolant line 130 or the low-temperature coolant line 140, at either end of the engine, such as at point A or B.
Furthermore, such a coolant circulation system typically includes a heater 180 for radiating heat into the interior of a vehicle. This heater 180 radiates heat of the coolant, supplied through the high-temperature coolant line 130, into the interior of the vehicle. In order to quickly radiate heat, a heater supply-line 185, for supplying coolant to the heater 180, is connected to the high-temperature coolant line 130 or to the cylinder head 110 (as shown). Where the thermostat 170 is disposed at the high-temperature coolant line 130, the heater supply-line 185 is connected to either the cylinder head 110, or between the engine and the thermostat 170. Where the thermostat 170 is disposed at the low-temperature coolant line 140, the heater supply-line 175 may be connected elsewhere.
Coolant is also supplied to a throttle body 190 that includes a throttle valve. The connection of a throttle body supply-line 195 for supplying coolant to the throttle body 190 is similar to the connection of the heater supply-line 185 described above.
In use, when the engine 100 is cool, the thermostat 170 closes the low-temperature coolant line 140 such that coolant flow to the radiator 150 is blocked. Accordingly the coolant circulates in the first and second water-jackets 115 and 125, the heater 180, and the throttle body 190 as shown by dotted arrows in FIG. 1. Once the engine 100 has warmed up such that the coolant temperature becomes a predetermined temperature (usually preset in the range of 82xc2x0 C. and 88xc2x0 C.), the thermostat 170 is opened such that the coolant can circulate through the radiator 150 as shown by solid arrows in FIG. 1. Because the cylinder head 110 is exposed to more heat than any other part in the internal combustion engine, more heat is conducted and radiated through the cylinder head 110. While the engine is warming up, coolant flows through the heater 180 and the throttle body 190. However, such coolant flows through the cylinder block 120, as well as the cylinder head 110, and accordingly heating efficiency to the interior of a vehicle is deteriorated. Furthermore, the warm-up period is lengthened.
In addition, during the warm-up period where the engine 100 is below a normal operating temperature, a catalytic converter, used for emission-control, does not sufficiently function to reduce noxious gas. Therefore, if the warm-up period is reduced, noxious exhaust gas may be reduced.
Furthermore, fuel consumption is increased during the warm-up period because lubricant temperature is low and its viscosity is high such that friction of mechanical parts of the engine 100 is high. Therefore, if the warm-up period is reduced, fuel consumption may also be lowered.
What is more, when the engine is warmed up to a normal operating temperature, the cylinder head 110 is exposed to substantially large amounts of heat. Therefore, heat from the cylinder head 110 should be more efficiently radiated. Furthermore, a cooling system and method of an engine should be preferably enhanced to reflect engine load, as radiation of heat is dependent on whether the engine load is high or low.
Embodiments of the present invention provide systems and methods for cooling an engine where a cylinder block and cylinder head are separately cooled. It should be appreciated that a xe2x80x9cthermostatxe2x80x9d as used here includes any device that acts as a valve, which is open at a temperature above a predetermined temperature, and closed at a temperature below the predetermined temperature. Also, a xe2x80x9cwater-jacketxe2x80x9d as used herein includes any kind of passage with any shape, for enabling flow of coolant.
The cooling systems described herein are preferably used for cooling an engine. The engine preferably includes a cylinder head and a cylinder block. The cylinder head includes a head water-jacket for circulating coolant, while the cylinder block includes a block water-jacket for circulating the coolant. An exemplary cooling system also preferably includes a radiator for cooling the coolant, a high-temperature coolant line for supplying the coolant from the cylinder head to the radiator, a low-temperature coolant line for supplying the coolant from the radiator to at least one of the head and block water-jackets, a first thermostat disposed at a predetermined position in either the low-temperature coolant line or the high-temperature coolant line, a branch coolant line for supplying the coolant from the block water-jacket to the high-temperature coolant line, a second thermostat disposed at the branch coolant line, and a hydraulic pump for generating coolant flow in the coolant lines. The head and block water-jackets communicate with each other via a primary pathway for transporting the coolant therebetween. Also, coolant flow is blocked within a cylinder-region, where the cylinder region is a region between the primary pathway and the branch coolant line.
The low-temperature coolant line preferably supplies the coolant to the block water-jacket. A bypass flow-line for bypassing the second thermostat is preferably formed at the branch coolant line and/or the second thermostat.
A flow-rate of the second thermostat is preferably smaller than a flow-rate of the first thermostat by a predetermined ratio. More specifically, the predetermined ratio is preferably preset such that the ratio of coolant flow passing through the head water-jacket and the block water-jacket lies within a range of 7:3 to 5:5.
The primary pathway is preferably formed near a circumference of a cylinder distal from where the coolant is exhausted from the head water-jacket to the high-temperature coolant line. Within the cylinder-region, at least one air hole is preferably formed between the head water-jacket and the block water-jacket. A secondary pathway is preferably provided for transporting the coolant between the head and block water-jackets. This secondary pathway is found at a more distal portion than the primary pathway from where the coolant is exhausted from the head water-jacket to the high-temperature coolant line. Where the first thermostat is disposed at the high-temperature coolant line, the branch coolant line connects the block water-jacket to the high temperature coolant line at a predetermined portion located toward the engine from the first thermostat. Where the low-temperature coolant line is connected to the branch coolant line, the low-temperature coolant line comprises a first low-temperature coolant line from the radiator to the branch coolant line and a second low-temperature coolant line from the branch coolant line to the hydraulic-pump. In this embodiment, the first thermostat, preferably disposed between the first low-temperature coolant line and the branch coolant line, comprises a main valve and a bypass valve being cooperatively connected. The second low-temperature coolant line is branched between the main valve and the bypass valve.
An exemplary cooling method according to an embodiment of the present invention includes determining if a coolant temperature in the head water-jacket is above a first predetermined temperature. The coolant in the head water-jacket is then supplied to a radiator when the coolant temperature in the head water-jacket is above the first predetermined temperature. It is then determined if a coolant temperature in the block water-jacket is above a second predetermined temperature. The coolant in the block water-jacket is supplied to a radiator when the coolant temperature in the block water-jacket is above the second predetermined temperature. The second predetermined temperature is preferably preset higher than the first predetermined temperature. When the coolant temperature in the block water-jacket is not above the second predetermined temperature, the coolant in the block water-jacket is preferably supplied to the radiator in a smaller amount than that supplied from the head water-jacket to the radiator when the coolant temperature in the head water-jacket is above the first predetermined temperature.